Multi-voltage power supply

ABSTRACT

A multi-voltage power supply includes a transformer, a first output circuit to generate a first output voltage using a voltage transferred to a secondary winding of the transformer, and a first output voltage controller to control a voltage supplied to the primary winding of the transformer according to the first output voltage. The multi-voltage power supply includes second through Nth output circuits to generate second through Nth output voltages using the voltage transferred to the secondary winding of the transformer, and second through Nth output voltage controllers performing control in order to linearly output the second through Nth output voltages by feeding back the second through Nth output voltages. Accordingly, multiple (at least two) output circuits, which are on the secondary winding side of the transformer, to realize multiple output voltages can be independently controlled, and in particular, by linearly controlling the multiple output circuits, the multiple output voltages can be stably controlled regardless of the number of output voltages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2005-0067631, filed on Jul. 26, 2005, in the Korean IntellectualProperty Office, the benefit of Korean Patent Application No.10-2006-0003284, filed on Jan. 11, 2006, in the Korean IntellectualProperty Office, and the benefit of Korean Patent Application No.10-2006-0058887, filed on Jun. 28, 2006, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to a multi-voltage powersupply, and more particularly, to a multi-voltage power supply toindependently control multiple voltages using a simple structure.

2. Description of the Related Art

In general, devices, such as personal computers (PCs), printers,photocopiers, monitors, and communication terminals, require aheavy-duty power supply system having a simple structure, a small size,and consistent power supply capability. Current source type powersupplies are generally used for this required heavy-duty power supplysystem.

FIG. 1 is a circuit diagram illustrating the basic operation of acurrent source type power supply called a “flyback converter,” which isa type of direct current (DC)/DC converter.

Referring to FIG. 1, the flyback converter includes a transformer Thaving a predetermined winding ratio, a primary circuit 10 connected tothe primary coil, i.e., the input coil, of the transformer T, and asecondary circuit 20 connected to the secondary coil, i.e., the outputcoil, of the transformer T. The primary circuit 10 and the secondarycircuit 20 are isolated from each other by the transformer T.

The primary circuit 10 includes a control switch S connected in seriesbetween the primary coil of the transformer T and ground. The controlswitch S controls a stored energy or a transfer operation of thetransformer T by switching an input voltage in response to a controlsignal input from an output voltage controller 30.

The secondary circuit 20 includes a rectifier 21 which is used torectify a current transferred from the transformer T. The rectifier 21includes a diode D and a capacitor C, which are connected in series, andtogether are connected in parallel to the secondary coil of thetransformer T. An output terminal is formed at the both ends of thecapacitor C. That is, an external load can be connected in parallel tothe capacitor C. The secondary circuit 20 also can include a filter (notillustrated) for filtering high frequency noise and Electro MagneticInterference (EMI) and an output voltage control circuit (notillustrated).

If the control switch S included in the primary circuit 10 is in an ONstate (closed), a voltage having a polarity opposite to that of theprimary coil of the transformer T is induced in the secondary coil,resulting in an inverse bias state of the diode D of the rectifier 21.Thus, a current flowing through the secondary circuit 20 is blocked, andenergy is stored in the form of a magnetization inductance of thetransformer T. That is, in an ON state (closed) of the control switch S,a current transfer by the transformer T is not performed, and the entireenergy supplied to the primary coil is stored in the form of themagnetization inductance of the transformer T.

If the control switch S is in an OFF state (open), a voltage, having apolarity opposite to when the control switch S is in the OFF state(open), is induced in the secondary coil of the transformer T, resultingin an ON state of the diode D of the secondary circuit 20. Thus, acurrent due to the magnetization inductance of the transformer T istransferred to the secondary circuit 20, and a DC voltage rectified bythe rectifier 21 is thereby output through the output terminal.

The output voltage controller 30 is connected to the output terminal ofthe secondary circuit 20. The output voltage controller 30 applies acontrol signal to the control switch S by feeding back the outputvoltage of the secondary circuit 20. The control signal acts as a signalfor controlling a duty rate of the control switch S. Thus, the outputvoltage can be controlled by controlling the operation of the controlswitch S.

As described above, by using the magnetization inductance component ofthe transformer T as a boost inductor, the flyback converter storesenergy in the form of the magnetization inductance of the transformer Twhen the control switch S included in the primary circuit 10 is in theOFF state, and supplies the rectified DC voltage by transferring thecurrent, due to the change in magnetization inductance, to the secondarycoil of the transformer T when the control switch S is in the ON state.

Thus, in terms of the secondary circuit 20, since the transformer T actsas a current source for supplying a current periodically, each powersupply having this principle is called a current source type powersupply. Various other types of current source type power supplies,besides the flyback converter, exist, according to various circuitconfigurations added to a primary circuit.

Since such a current source type power supply has a secondary circuitwith a simpler rectifier structure and less components compared to othertype power supplies, the current source type power supply has anadvantage when used to output multiple voltages. That is, sincesecondary circuits corresponding to the multiple voltages must beincluded, if the secondary circuits have a simple structure, a totalsize of a power supply can be reduced.

Due to this advantage, various current source type multi-voltage powersupplies have been suggested. However, since conventional current sourcetype multi-voltage power supplies use a plurality of transformers and aplurality of inefficient regulator chips to control output voltages ofsecondary circuits, and/or have a complex structure in which an outputvoltage feedback circuit of each secondary circuit is connected to aprimary circuit, the advantage of the current source type power suppliescannot be properly utilized.

SUMMARY OF THE INVENTION

The present general inventive concept provides a multi-voltage powersupply having a simple structure and a significantly small size, whichincludes a plurality of output circuits on a secondary winding side of atransformer, whereby an output voltage of each of the output circuits iscontrolled independently.

Additional aspects and utilities of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

The foregoing and/or other aspects and utilities of the present generalinventive concept are achieved by providing a multi-voltage power supplyincluding a transformer, a first output circuit to generate a firstoutput voltage using a voltage transferred to a secondary winding sideof the transformer, and a first output voltage controller to control avoltage supplied to a primary winding of the transformer according tothe first output voltage, the multi-voltage power supply including:second through N^(th) output circuits to generate second through N^(th)output voltages, respectively, using the voltage transferred to thesecondary winding of the transformer; and second through N^(th) outputvoltage controllers to control linearly outputting the second throughN^(th) output voltages, respectively, by feeding back the second throughN^(th) output voltages.

The foregoing and/or other aspects and utilities of the present generalinventive concept are also achieved by providing a multi-voltage powersupply including a transformer, a first output circuit to generate afirst output voltage using a voltage transferred to a secondary windingof a transformer, and a first output voltage controller to control avoltage supplied to a primary winding of the transformer according tothe first output voltage, the multi-voltage power supply including:second through N^(th) output circuits to generate second through N^(th)output voltages, respectively, using the voltage transferred to thesecondary winding of the transformer; and second through N^(th) outputvoltage controllers to control outputting the second through N^(th)output voltages, respectively, according to a switching operation byfeeding back the second through N^(th) output voltages.

The foregoing and/or other aspects and utilities of the present generalinventive concept are also achieved by providing a method of providing amulti-voltage power supply using a transformer, the method includinggenerating a first output voltage using a voltage transferred to asecondary winding of the transformer; controlling a voltage supplied toa primary winding of the transformer according to the first outputvoltage; generating second through N^(th) output voltages using thevoltage transferred to the secondary winding of the transformer; andcontrolling to linearly output the second through N^(th) output voltagesby feeding back the second through N^(th) output voltages.

The foregoing and/or other aspects and utilities of the present generalinventive concept are also achieved by providing a method of providing amulti-voltage power supply using a transformer, the method includinggenerating a first output voltage using a voltage transferred to asecondary winding of the transformer; controlling a voltage supplied toa primary winding of the transformer according to the first outputvoltage; generating second through N^(th) output voltages using thevoltage transferred to the secondary winding of the transformer; andcontrolling outputting the second through N^(th) output voltagesaccording to a switching operation by feeding back the second throughN^(th) output voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a circuit diagram illustrating a basic operation of aconventional current source type power supply;

FIG. 2 is a circuit diagram of a multi-voltage power supply according toan embodiment of the present general inventive concept;

FIG. 3 is a graph illustrating a linear switching operation of a secondswitch of the multi-voltage power supply of FIG. 2, according to anembodiment of the present general inventive concept;

FIG. 4 is an equivalent circuit diagram of the second switch of themulti-voltage power supply of FIG. 2, which is controlled according to avariation of a linear control signal, according to an embodiment of thepresent general inventive concept;

FIG. 5 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 2, according toan embodiment of the present general inventive concept;

FIG. 6 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept;

FIG. 7 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept;

FIG. 8 is a circuit diagram of a different type of multi-voltage powersupply, which can be derived from the multi-voltage power supply of FIG.7, according to an embodiment of the present general inventive concept;

FIG. 9 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept;

FIG. 10 is a circuit diagram of a different type of multi-voltage powersupply, which can be derived from the multi-voltage power supply of FIG.9, according to an embodiment of the present general inventive concept;

FIG. 11 is a circuit diagram of a multi-voltage power supply accordingto another embodiment of the present general inventive concept;

FIG. 12 is a circuit diagram of a multi-voltage power supply accordingto another embodiment of the present general inventive concept;

FIG. 13 is a circuit diagram of a second output voltage controller ofthe multi-voltage power supply of FIG. 12, according to an embodiment ofthe present general inventive concept;

FIG. 14 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12, according toan embodiment of the present general inventive concept;

FIG. 15 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12, according toanother embodiment of the present general inventive concept;

FIG. 16 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12, according toanother embodiment of the present general inventive concept; and

FIGS. 17A and 17B are photographs of a conventional active clamp typepower supply and an active clamp type power supply according to anembodiment of the present general inventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to the likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures.

FIG. 2 is a circuit diagram of a multi-voltage power supply, i.e., acurrent source type two-voltage power supply, according to an embodimentof the present general inventive concept. Although a two-voltage powersupply is described in the current embodiment, a multi-voltage powersupply can be configured to output N (N is a natural number) outputvoltages according to an implementation environment. If the number ofoutput voltages is N, a transformer includes N secondary coils, and asecondary output circuit can be connected to each of the N secondarycoils.

Referring to FIG. 2, the multi-voltage power supply includes atransformer T having a primary coil L1 and two secondary coils, i.e., afirst coil L2 and a second coil L3, forming predetermined winding ratioswith the primary coil L1. A primary circuit 110 is connected to theprimary coil L1, a first output circuit 120 is connected to the firstcoil L2 in the secondary winding, and a second output circuit 140 isconnected to the second coil L3 in the secondary winding. The primarycircuit 110 is isolated from the first and second output circuits 120and 140 of the secondary winding by the transformer T.

The primary circuit 110 includes a current source type switching circuit111 connected to the primary coil L1 of the transformer T. The currentsource type switching circuit 111 controls a stored energy or transferoperation of the transformer T by performing a switching operation inresponse to a first control signal applied by a first output voltagecontroller 130.

The current source type switching circuit 111 can include a firstcontrol switch S1 connected between the primary coil L1 of thetransformer T and ground.

If the first control switch S1 is in an ON state (closed), a voltagehaving a polarity opposite to that of the primary coil L1 of thetransformer T is induced in the secondary coils L2 and L3, resulting inan inverse bias state of diodes D1 and D2 included in the first andsecond output circuits 120 and 140, and accordingly, currents flowingthrough the first and second output circuits 120 and 140 are blocked,and energy is stored in the form of a magnetization inductance of thetransformer T.

If the first control switch S1 is in an OFF state (open), a voltagehaving a polarity opposite to when the first control switch S1 is in theOFF state (open), is induced to the secondary coils L2 and L3 of thetransformer T, resulting in an ON state of the diodes D1 and D2 includedin the first and second output circuits 120 and 140, and accordingly, acurrent due to the magnetization inductance of the transformer T istransferred to the first and second output circuits 120 and 140.

The first output circuit 120 generates a first output voltage V_(o1) byrectifying a voltage transferred to the secondary winding of thetransformer T. For the rectification, the first output circuit 120includes a first rectifier 121 to rectify the voltage. The firstrectifier 121 illustrated in FIG. 2 is a half-wave rectifier. In thepresent embodiment, the first output circuit 120 may include a half-waveor full-wave rectifier.

The first rectifier 121 can include the first diode D1 and a firstcapacitor C1, which are connected in series, and together are connectedin parallel to the first coil L2 in the secondary winding of thetransformer T. In this case, a first output terminal used to output thefirst output voltage V_(o1) can be formed at both ends of the firstcapacitor C1.

The first output voltage controller 130 can control a voltage suppliedto the primary winding of the transformer T according to the firstoutput voltage V_(o1) generated by the first output circuit 120. Thefirst output voltage controller 130 applies the first control signal tothe first control switch S1 by feeding back the first output voltageV_(o1). Herein, the first control signal indicates a signal to control aduty rate of the first control switch.

The second output circuit 140 generates a second output voltage V_(o2)by rectifying the voltage transferred from the transformer T. For therectification, the second output circuit 140 includes a second rectifier141 and a second switch Q2.

The second rectifier 141 can include the second diode D2 and a secondcapacitor C2, which are connected in series, and together are connectedin parallel to the second coil L3 in the secondary winding of thetransformer T, in order to generate the second output voltage V_(o2) byrectifying the voltage transferred from the transformer T. In this case,a second output terminal used to output the second output voltage V_(o2)can be formed at both ends of the second capacitor C2.

The second switch Q2 linearly switches an operation of the secondrectifier 141 in an active region in response to a linear control signalCtrl2 applied from a second output voltage controller 160. For theswitching operation, the second switch Q2 is disposed between the seconddiode D2 and the second capacitor C2. The second switch Q2 can beimplemented using a metal oxide semiconductor field effect transistor(MOSFET), a gate of which is connected to an output terminal of thesecond output voltage controller 160, or a bipolar junction transistor(BJT). If the second switch Q2 is implemented using a MOSFET, the secondswitch Q2 linearly switches an operation of the second rectifier 141 byreceiving the linear control signal Ctrl2 through the gate of theMOSFET.

FIG. 3 is a graph illustrating a linear switching operation of thesecond switch Q2 of the multi-voltage power supply of FIG. 2, accordingto an embodiment of the present general inventive concept. If it isassumed that a current flowing through the second switch Q2 is I and avoltage across the second switch Q2 is V, a correlation illustrated inFIG. 3 is formed between the current I and the voltage V. Referring toFIG. 3, the second switch Q2 performs a switching operation in an activeregion, i.e., a region in which a curve becomes linear, not in asaturation region. The switching operation in the active region iscalled a linear switching operation.

The second output voltage controller 160 linearly controls the secondoutput voltage V_(o2) independently of the first output voltagecontroller 130 by generating the linear control signal Ctrl2 to controlthe second switch Q2 operating in the active region by feeding back thesecond output voltage V_(o2) and applying the generated linear controlsignal Ctrl2 to the second switch Q2.

The second output voltage controller 160 can include a reference voltagegenerator 161, an error detector 162, a compensation circuit 163, and acontrol signal output unit 164.

The reference voltage generator 161 generates a reference voltage to becompared to the second output voltage V_(o2) and outputs the generatedreference voltage to the error detector 162. The reference voltagegenerator 161 can include a first reference voltage generator, which isconnected to a predetermined voltage source V_(c) and generates a firstreference voltage, and a voltage divider circuit to generate a secondreference voltage by voltage-dividing the first reference voltage.

The first reference voltage generator includes a third resistor R3connected to the voltage source V_(c) and a zener diode DZ. At a node A,the first reference voltage (i.e., a value obtained by adding apredetermined voltage, e.g., 2.5 V, to the second output voltage V_(o2))can be generated by the third resistor R3 and the zener diode DZ. Thatis, a voltage generated at the node A is V_(o2)+2.5 V.

The voltage divider circuit includes a first resistor R1 and a secondresistor R2, which voltage-divide the first reference voltage generatedby the first reference voltage generator. At a node B located betweenthe first resistor R1 and the second resistor R2, the second referencevoltage having a value “(V_(o2)+2.5)×(R1/(R1+R2))” according to avoltage dividing formula is generated. The generated second referencevoltage is input to a first input terminal of the error detector 162.

Thus, the second reference voltage is input to the first input terminalof the error detector 162, and the second output voltage V_(o2) is inputto a second input terminal of the error detector 162. The error detector162 compares the input second reference voltage and second outputvoltage V_(o2) and outputs a difference value, i.e., an error value.

The error detector 162 can be realized using a comparator. In this case,since two input terminals of the comparator are in a virtual shortstate, the voltage at the node B can be considered in a normal state thesame as a voltage at a node C, which is the second output voltageV_(o2). Thus, since the voltage at the node B is the same as the voltageat the node C, Equation 1 can be realized as provided below.V _(o2)=(V _(o2)+2.5)×(R1/(R1+R2))  (1)

Thus, the second output voltage V_(o2) can be simplified to Equation 2as provided below.V _(o2)=2.5×(R1/R2)  (2)

That is, the second output voltage V_(o2) to be controlled can bedetermined by a zener value and resistances of the first and secondresistors R1 and R2.

The compensation circuit 163 stabilizes the second output voltagecontroller 160 by providing a compensation circuit for negativefeedback. The compensation circuit 163 may include a fourth resistor R4and a capacitor C_(p) connected in series with each other, which aretogether connected in parallel to the second input terminal and anoutput terminal of the error detector 162.

The control signal output unit 164 outputs the second control signalCtrl2 by voltage-dividing an error value output from the error detector162 in order to linearly control the second switch Q2 operating in theactive region. The control signal output unit 164 can include fifth andsixth resistors R5 and R6 for voltage-dividing the error value. Thus,the linear control signal Ctrl2 output through the control signal outputunit 164 can be presented using Equation 3 provided below.Ctrl2=V _(err)×(R6/(R5+R6))  (3)

Herein, V_(err) denotes the error value output from the error detector162.

Thus, a gate voltage of the second switch Q2 has a value“V_(err)×(R6/(R5+R6))”. Appropriate values for the resistances of thefifth and sixth resistors R5 and R6 can be determined in order for thesecond switch Q2 to operate in the active region. Thus, the gate voltageof the second switch Q2 varies in the active region according to theerror value output from the error detector 162, thereby varying anequivalent drain-source resistance of the second switch Q2.

FIG. 4 is an equivalent circuit diagram of the second switch Q2 of themulti-voltage power supply of FIG. 2, which is controlled according to avariation of the linear control signal Ctrl2, according to an embodimentof the present general inventive concept. As illustrated in FIG. 4, thesecond switch Q2 can be represented by a variable resistor R_(ds), theresistance of which varies according to the linear control signal Ctrl2.Thus, since a current flowing through the second diode D2 varies inresponse to the linear control signal Ctrl2 varying according to avariation of the second output voltage V_(o2), the second output voltageV_(o2) can be controlled.

The multi-voltage power supply according to the embodiments of thepresent general inventive concept can use various type circuits. Forexample, a current source type switching circuit of a primary circuitcan be configured using an active clamp flyback type, a half-bridgeflyback type, or a series resonance type, besides the flyback typeillustrated in FIG. 2. Thus, in the embodiments described below,multi-voltage power supplies, in which each of these various currentsource type switching circuits is applied to a primary circuit, will bedescribed.

FIG. 5 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 2, according toan embodiment of the present general inventive concept. Referring toFIG. 5, if a load on the side of the second output circuit 140 decreasesat a time t2, the second output voltage V_(o2) exceeds a maximum limitvoltage V_(o) _(—) _(max). At this time, the linear control signal Ctrl2of the second output voltage controller 160 is the same as the gatevoltage V_(gQ2) of the second switch Q2 and controls the second outputvoltage V_(o2) by decreasing the gate voltage V_(gQ2) so that the secondswitch Q2 operates in the active region. That is, like V_(dsQ2), whichis the voltage across the second switch Q2, the second switch Q2 acts asa variable resistor by causing a constant voltage decrease from the timet2. In FIG. 5, I_(D2) denotes the current flowing through the seconddiode D2.

FIG. 6 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept. In FIG. 6,a current source type switching circuit 311 is configured as the activeclamp flyback type.

The current source type switching circuit 311 of a primary circuit 310illustrated in FIG. 6 has a structure to which an active snubbercircuit, which is used to prevent a switching loss due to a leakageinductance of a transformer T, is added.

That is, the current source type switching circuit 311 is connected inparallel to a primary coil of the transformer T and includes a capacitorC_(c) and a second control switch S2 connected in series. Herein, thesecond control switch S2 and a first control switch S1 operatecomplementarily and have a short dead time.

If the first control switch S1 is in an ON state, energy is stored inthe transformer T, and if the first control switch S1 is in an OFFstate, the energy stored in the transformer T is transferred to firstand second output circuits 120 and 140 on a secondary winding side ofthe transformer T. The energy stored in the form of a leakage inductanceand a magnetization inductance of the transformer T allows the secondcontrol switch S2 and the first control switch S1 to perform zerovoltage switching. In addition, the capacitor C_(c) connected in serieswith the second control switch S2 resonates with the leakage inductanceof the transformer T while a current flows through the secondary windingof the transformer T.

FIG. 7 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept. In FIG. 7,a current source type switching circuit 411 is configured as thehalf-bridge flyback type.

The current source type switching circuit 411 of a primary circuit 410illustrated in FIG. 7 can include a first control switch S1 and a secondcontrol switch S2. The first control switch S1 and the second controlswitch S2 operate complementarily and have a short dead time. If thefirst control switch S1 is in an ON state, energy is stored in atransformer T, and if the first control switch S1 is in an OFF state,the energy stored in the transformer T is transferred to first andsecond output circuits 120 and 140 on a secondary winding side of thetransformer T.

In addition, a capacitor C_(b) connected in series with a primary coilof the transformer T charges or discharges energy according to adirection of a current flowing through the primary coil of thetransformer T and resonates with a leakage inductance of the transformerT while a current flows through the secondary winding of the transformerT.

FIG. 8 is a circuit diagram of a different type of multi-voltage powersupply, which can be derived from the multi-voltage power supply of FIG.7, according to an embodiment of the present general inventive concept.Since an operation of a current source type switching circuit 411′ of aprimary circuit 410′ illustrated in FIG. 8 is almost the same as that ofthe current source type switching circuit 411 illustrated in FIG. 7, adetailed description is omitted.

FIG. 9 is a circuit diagram of a multi-voltage power supply according toanother embodiment of the present general inventive concept. In FIG. 9,a current source type switching circuit 511 is configured as the seriesresonance type. Referring to FIG. 9, the current source type switchingcircuit 511 of a primary circuit 510 can include a first control switchS1 and a second control switch S2. The first control switch S1 and thesecond control switch S2 operate complementarily and have a short deadtime. In addition, an inductor L_(r) connected in series with acapacitor C_(e) corresponds to a leakage inductance of the transformer Tor an additional inductor in the outside of the transformer T.

While the first control switch S1 is in an ON or OFF state, thecapacitor C_(e) and the inductor L_(r) resonate with each other, andenergy is transferred to the circuits on the secondary winding side bythe transformer T operating as a current source.

FIG. 10 is a circuit diagram of a different type of multi-voltage powersupply, which can be derived from the multi-voltage power supply of FIG.9, according to an embodiment of the present general inventive concept.

In the above embodiments, multi-voltage power supplies having variouscurrent source type switching circuits are described. A multi-voltagepower supply having a full-wave rectification circuit, in which a firstoutput circuit on a secondary winding side of a transformer can performfull-wave rectification, will now be described.

FIG. 11 is a circuit diagram of a multi-voltage power supply accordingto another embodiment of the present general inventive concept.Referring to FIG. 11, a first output circuit 710 includes a full-waverectifier 711.

The first output circuit 710 has two current paths in order to performfull-wave rectification on a current transferred from a transformer T,and the current paths respectively include diodes D1 or D1′. Thus, thecurrent paths perform rectification by alternatively conductingaccording to switching performed by a current source type switchingcircuit 111, thereby outputting a full-wave rectified first outputvoltage V_(o1)′.

In the above-described embodiments, each of the multi-voltage powersupplies can independently control a plurality of output circuits on asecondary winding side of a transformer using second through N^(th)output voltage controllers having a simple structure. According to theconfigurations of the above-described embodiments, the size of eachmulti-voltage power supply can be significantly reduced compared toconventional current source type power supplies. According to currentsource type power supplies implemented herein, it was confirmed that thesize of the overall multi-voltage power supply circuits is significantlyreduced and output voltages can be independently controlled.

FIG. 12 is a circuit diagram of a multi-voltage power supply accordingto another embodiment of the present general inventive concept. Althougha two-voltage power supply is described in the current embodiment, amulti-voltage power supply can be configured to output N (N is a naturalnumber) output voltages according to an implementation environment. Ifthe number of output voltages is N, a transformer includes N secondarycoils, and a secondary output circuit can be connected to each of the Nsecondary coils.

Referring to FIG. 12, the multi-voltage power supply includes atransformer T having a primary coil L1 and two secondary coils, i.e., afirst coil L2 and a second coil L3, forming predetermined winding ratioswith the primary coil L1. A primary circuit 110 is connected to theprimary coil L1, a first output circuit 120 is connected to the firstcoil L2 in the secondary winding, and a second output circuit 140 isconnected to the second coil L3 in the secondary winding. The primarycircuit 110 is isolated from the first and second output circuits 120and 140 of the secondary winding by the transformer T. The primarycircuit 110 includes a current source type switching circuit 111connected to the primary coil L1 of the transformer T. The currentsource type switching circuit 111 controls a stored energy or transferoperation of the transformer T by performing a switching operation inresponse to a first control signal applied by a first output voltagecontroller 130. The current source type switching circuit 111 caninclude a first control switch S1 connected between the primary coil L1of the transformer T and a ground. Since the current source typeswitching circuit 111 is the same as the above description, a detaileddescription is omitted.

The first output circuit 120 generates a first output voltage V_(o1) byrectifying a voltage transferred to the secondary winding of thetransformer T. For the rectification, the first output circuit 120includes a first rectifier 121 to rectify the voltage. The firstrectifier 121 illustrated in FIG. 12 is a half-wave rectifier. In thepresent embodiment, the first output circuit 120 may include a half-waveor full-wave rectifier. Since the first output circuit 120 is the sameas the first output circuit 120 described above, a detailed descriptionis omitted.

The first output voltage controller 130 controls a voltage supplied tothe primary winding of the transformer T according to the first outputvoltage V_(o1) generated by the first output circuit 120. Since thefirst output voltage controller 130 is the same as the first outputvoltage controller 130 described above, a detailed description isomitted.

The second output circuit 140 generates a second output voltage V_(o2)by rectifying the voltage transferred from the transformer T. For therectification, the second output circuit 140 includes a second rectifier141 and a second switch Q2.

The second rectifier 141 can include a second diode D2 and a secondcapacitor C2, which are connected in series, and together are connectedin parallel to the second coil L3 in the secondary winding of thetransformer T, in order to generate the second output voltage V_(o2) byrectifying the voltage transferred from the transformer T. In this case,a second output terminal to output the second output voltage V_(o2) canbe formed at both ends of the second capacitor C2.

The second switch Q2 switches an operation of the second rectifier 141in an active region in response to a switching control signal Ctrl2applied from a second output voltage controller 180. For the switchingoperation, the second switch Q2 is disposed between the second diode D2and the second capacitor C2. The second switch Q2 can be implementedusing a MOSFET, a gate of which is connected to an output terminal ofthe second output voltage controller 180, or a BJT. If the second switchQ2 is implemented using a MOSFET, the second switch Q2 switches anoperation of the second rectifier 141 by receiving the linear switchingcontrol signal Ctrl2 through the gate of the MOSFET.

The second output voltage controller 180 independently controls thesecond output voltage V_(o2) by generating the switching control signalCtrl2 to control the second switch Q2 by feeding back the second outputvoltage V_(o2) and applying the generated switching control signal Ctrl2to the second switch Q2. The switching control signal Ctrl2 will bedescribed in detail later.

FIG. 13 is a circuit diagram of the second output voltage controller 180of the multi-voltage power supply of FIG. 12, according to an embodimentof the present general inventive concept. Referring to FIG. 13, thesecond output voltage controller 180 can include an output voltagedetector 181, an error detector 182, a compensation circuit 183, afrequency synchronization unit 184, and a pulse width modulator (PWM)185.

The output voltage detector 181 detects the second output voltage V_(o2)in accordance with a predetermined voltage ratio and outputs thedetected voltage to the error detector 182. The output voltage detector181 can include a voltage divider circuit including two resistors, i.e.,a first resistor R1 and a second resistor R2.

A predetermined reference voltage V_(ref), e.g., 2.5 V, is input to afirst input terminal of the error detector 182. The reference voltageV_(ref) can be generated by a third resistor R3 connected between avoltage source V_(c) and ground via a zener diode DZ. The voltagedetected by the output voltage detector 181 is input to a second inputterminal of the error detector 182.

The compensation circuit 183 stabilizes the second output voltagecontroller 180 by providing a compensation circuit using negativefeedback. The compensation circuit 183 may include a fourth resistor R4and a capacitor C_(p) connected in series with each other, which aretogether connected in parallel to the second input terminal and anoutput terminal of the error detector 182.

The frequency synchronization unit 184 synchronizes a predetermined rampsignal input from the outside with a synch signal detected from afront-end of the second diode D2. The synch signal can denote a squarewave having the same frequency as a switching frequency of the firstcontrol switch S1 of the primary circuit 110. The ramp signal can denotea signal having a predetermined ramp waveform.

The PWM 185 generates the switching control signal Ctrl2 to controlON/OFF of the second switch Q2 by comparing a signal, i.e., an amplifiederror value, provided by the error detector 182, to the synchronizedramp signal output from the frequency synchronization unit 184 andapplies the generated switching control signal Ctrl2 to the secondswitch Q2. Herein, the switching control signal Ctrl2 is generated inthe same period as that of the synchronized ramp signal, and a delay ofthe switching control signal Ctrl2 is controlled according to the errorvalue provided by the error detector 182.

Thus, by feeding back the second output voltage V_(o2) and controllingON/OFF states of the current flowing through the second diode D2according to the amplitude of the detected second output voltage V_(o2)by using the second output voltage controller 180, the amplitude of acurrent provided to an output terminal of the second output circuit 140can be controlled, thereby controlling the second output voltage V_(o2)to have a desired amplitude.

FIG. 14 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12, according toan embodiment of the present general inventive concept.

In FIG. 14, VgS1 denotes a voltage across the first control switch S1,and VgQ2 denotes a gate-source voltage of the second switch Q2. In otherwords, VgS1 and VgQ2 indicate operation states of the first controlswitch S1 and the second switch Q2, respectively. For example, if VgS1or VgQ2 has a high level value, the first control switch S1 or thesecond switch Q2 is in an ON state, and if VgS1 or VgQ2 has a low levelvalue, the first control switch S1 or the second switch Q2 is in an OFFstate. In addition, Ts denotes a switching period of the first controlswitch S1, and Td denotes a delay time of the second switch Q2.

Referring to FIGS. 12 through 14, an operation of the first controlswitch S1 can be divided into an ON state duration (between t_(a) andt_(b)) and an OFF state duration (between t_(b) and t_(d)) and the ONand OFF state durations are repeated in the period Ts. The second switchQ2 to control the second output voltage V_(o2) repeats ON and OFF statesin the same period Ts as the first control switch S1 due to thesynchronization. Thus, the second output voltage V_(o2) can becontrolled by properly controlling an ON state duration (between t_(b)and t_(c)) of the second switch Q2 from when a current is transferred tothe first and second output circuits 120 and 140 on the second windingside of the transformer T.

If the first control switch S1 is in an ON state, a magnetizationinductance current I_(m) of the transformer T linearly increases,resulting in storage of energy in the form of the magnetizationinductance of the transformer T. In this case, a current I_(d1) flowingthrough the first diode D1 of the first output circuit 120 on the secondwinding side of the transformer T, a current I_(d2) flowing through thesecond diode D2 of the second output circuit 140 on the second windingside of the transformer T, and a current I_(Q2) flowing through thesecond switch Q2 are all 0.

If the first control switch S1 is in an OFF state, a current due to themagnetization inductance of the transformer T is transferred to thefirst output circuit 120 in the second winding, and the current Id,flowing through the first diode D1 linearly decreases. Thus, the firstoutput voltage V_(o1) is output.

The second switch Q2 turns ON after a predetermined delay time haselapsed according to a feedback value of the second output voltageV_(o2) by control of the second output voltage controller 180, andtherefore, a current flows through the second diode D2, therebyoutputting the second output voltage V_(o2). If the first control switchS1 turns ON again, even if the second switch Q2 is ON, the currentsI_(d2) and I_(Q2) do not flow since the second diode D2 is in an inversebias state.

FIG. 15 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12, according toanother embodiment of the present general inventive concept.

Referring to FIG. 15, an operation of the first control switch S1 can bedivided into an ON duration (between t_(a) and t_(b)) and an OFFduration (between t_(b) and t_(d)) and the ON and OFF durations arerepeated in the period Ts. The second switch Q2 to control the secondoutput voltage V_(o2) repeats ON and OFF in the same period Ts as thefirst control switch S1 due to the synchronization.

In the ON duration (between t_(a) and t_(b)) of the first control switchS1, since a current is not transferred to the secondary winding, anoperation of the second switch Q2 does not influence an operation of themulti-voltage power supply. In the OFF duration (between t_(b) andt_(d)) of the first control switch S1, the second output voltage V_(o2)can be controlled by controlling the timing of a time t_(c) at which thesecond switch Q2 is in an OFF state according to a feedback value of thesecond output voltage V_(o2).

As described above, according to the present embodiment, by delaying theON or OFF operation state of the second switch Q2 according to thefeedback value of the second output voltage V_(o2) the amount of acurrent flowing through the second output circuit 140 on the secondwinding side of the transformer T can be controlled, therebyindependently controlling the second output voltage V_(o2). Thus, amulti-voltage current source type power supply having a simple structurecan be provided.

FIG. 16 is a timing diagram illustrating signal transitions according toan operation of the multi-voltage power supply of FIG. 12 when thecurrent source type switching circuit 111 of the primary circuit 110 isconfigured as the active clamp flyback type, according to anotherembodiment of the present general inventive concept.

In FIG. 16, VgS1 denotes a voltage across the first control switch S1,VgS2 denotes a voltage across the second control switch S2, and VgQ2denotes a gate-source voltage of the second switch Q2. In other words,VgS1, VgS2, and VgQ2 indicate operation states of the first controlswitch S1, the second control switch S2, and the second switch Q2,respectively.

Referring to FIGS. 12 and 16, an operation of the first control switchS1 can be divided into an ON duration (between t_(a) and t_(b)) and anOFF duration (between t_(b) and t_(d)) and the ON and OFF durations arerepeated during the period Ts. The second control switch S2 repeats ONand OFF durations complementarily with the first control switch S1. Thesecond switch Q2 to control the second output voltage V_(o2) repeats ONand OFF durations in the same period Ts as the first control switch S1due to the synchronization.

The second output voltage V_(o2) can be controlled by properlycontrolling a delay time Td in an ON duration (between t_(b) and t_(c))of the second switch Q2 from when a current is transferred to the firstand second output circuits 120 and 140 on the second winding side of thetransformer T. In the OFF duration (between t_(b) and t_(d)) of thefirst control switch S1, the second control switch S2 is in an ON stateand I_(s2) increases, and thereby the leakage inductance resonatesthrough the capacitor C_(c).

FIGS. 17A and 17B are photographs of a conventional active clamp typemulti-voltage power supply and an active clamp type multi-voltage powersupply according to an embodiment of the present general inventiveconcept. FIG. 17A illustrates a shape of the conventional active clamptype multi-voltage power supply, and FIG. 17B illustrates a shape of theactive clamp type multi-voltage power supply according to an embodimentof the present general inventive concept. Referring to FIGS. 17A and17B, the active clamp type multi-voltage power supply illustrated inFIG. 17B has a smaller size and a simpler structure than theconventional active clamp type multi-voltage power supply illustrated inFIG. 17A.

Although the number of output circuits in the secondary winding isillustrated as 2 in the various embodiments described above, it will beunderstood by those of ordinary skill in the art that a plurality ofoutput circuits on the secondary winding side of the transformer, whichare independently controlled, can be configured.

As described above, in a multi-voltage power supply according to thevarious embodiments of the present general inventive concept, sincemultiple (at least two) output circuits which are on a secondary windingside of a transformer, for realizing multiple output voltages can beindependently controlled, a structure of the output circuits is simple,and a size of the multi-voltage power supply can be significantlyreduced. In addition, by linearly controlling the multiple outputcircuits, the multiple output voltages can be stably controlledregardless of the number of output voltages.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

1. A multi-voltage power supply including a transformer, a first outputcircuit to generate a first output voltage using a voltage transferredto a secondary winding of the transformer, and a first output voltagecontroller to control a voltage supplied to a primary winding of thetransformer according to the first output voltage, the multi-voltagepower supply comprising: second through N^(th) output circuits togenerate second through N^(th) output voltages, respectively, using thevoltage transferred to the secondary winding of the transformer; andsecond through N^(th) output voltage controllers to control linearlyoutputting the second through N^(th) output voltages, respectively, byfeeding back the second through N^(th) output voltages, wherein a K^(th)(K is a positive integer greater than or equal to 2 and less than orequal to N) output circuit, which is one of the second through N^(th)output circuits, comprises: a K^(th) rectifier to generate a K^(th)output voltage by rectifying the voltage transferred from thetransformer; and a K^(th) switch to linearly switch an output voltage ofthe K^(th) rectifier according to a linear control signal of a K^(th)output voltage controller, which is one of the second through N^(th)output voltage controllers.
 2. The multi-voltage power supply of claim1, wherein the K^(th) rectifier comprises a K^(th) diode and a K^(th)capacitor, which are connected in series, and together are connected inparallel to the secondary winding of the transformer, and a K^(th)output terminal is formed at both ends of the K^(th) capacitor to outputthe K^(th) output voltage.
 3. The multi-voltage power supply of claim 1,wherein the K^(th) rectifier is either a half-wave rectification circuitor a full-wave rectification circuit.
 4. The multi-voltage power supplyof claim 2, wherein the K^(th) switch comprises a metal oxidesemiconductor field effect transistor (MOSFET), a gate of which isconnected to an output terminal of the K^(th) output voltage controllerand the other terminals of which are connected between the K^(th) diodeand the K^(th) capacitor.
 5. The multi-voltage power supply of claim 2,wherein the K^(th) switch comprises a bipolar junction transistor (BJT).6. The multi-voltage power supply of claim 2, wherein the K^(th) switchoperates in an active region in which a curve becomes linear in a graphshowing a correlation between a current flowing through the K^(th)switch and a voltage across the K^(th) switch.
 7. The multi-voltagepower supply of claim 1, wherein the K^(th) (K is a positive integergreater than or equal to 2 and less than or equal to N) output voltagecontroller, which is one of the second through N^(th) output voltagecontrollers, comprises: a K^(th) reference voltage generator to generatea predetermined reference voltage to be compared to a K^(th) outputvoltage; a K^(th) error detector to compare the K^(th) output voltage tothe reference voltage generated by the^(th) reference voltage generatorand output an error value according to the comparison result; and aK^(th) control signal output unit to output the K^(th) linear controlsignal to control the K^(th) switch in the active region byvoltage-dividing the signal output from the K^(th) error detector. 8.The multi-voltage power supply of claim 7, wherein the K^(th) referencevoltage generator comprises a voltage divider circuit, which isconnected to a predetermined voltage source and provides the referencevoltage to the K^(th) error detector by voltage-dividing a voltage ofthe predetermined voltage source.
 9. The multi-voltage power supply ofclaim 7, wherein the K^(th) control signal output unit comprises avoltage divider circuit to voltage-divide the signal output from theK^(th) error detector.
 10. The multi-voltage power supply of claim 7,wherein the K^(th) output voltage controller further comprises a K^(th)compensation circuit to provide a compensation circuit using negativefeedback, the K^(th) compensation circuit being connected in parallel toan output terminal of the K^(th) error detector and an input terminal ofthe K^(th) error detector to which the K^(th) output voltage is appliedand comprising a resistor and a capacitor, which are connected inseries.
 11. The multi-voltage power supply of claim 1, wherein thetransformer comprises a primary circuit having a current source typeswitching circuit, which comprises a first switch to perform a switchingoperation using a first control signal input from the first outputvoltage controller.
 12. The multi-voltage power supply of claim 11,wherein the current source type switching circuit is configured as oneof a flyback type, an active clamp flyback type, a half-bridge flybacktype, and a series resonance type.
 13. The multi-voltage power supply ofclaim 11, wherein the current source type switching circuit furthercomprises a snubber circuit to prevent a leakage inductance of thetransformer.
 14. The multi-voltage power supply of claim 1, wherein thefirst output circuit comprises a rectifier to rectify the voltagetransferred from the transformer.
 15. The multi-voltage power supply ofclaim 14, wherein the rectifier is either a half-wave rectificationcircuit or a full-wave rectification circuit.
 16. An image formingdevice comprising a multi-voltage power supply including a transformer,a first output circuit to generate a first output voltage using avoltage transferred to a secondary winding of the transformer, and afirst output voltage controller to control a voltage supplied to aprimary winding of the transformer according to the first outputvoltage, the multi-voltage power supply comprising: second throughN^(th) output circuits to generate second through N^(th) outputvoltages, respectively, using the voltage transferred to the secondarywinding of the transformer; and second through N^(th) output voltagecontrollers to control linearly outputting the second through N^(th)output voltages, respectively, by feeding back the second through^(th)output voltages, wherein a K^(th) (K is a positive integer greater thanor equal to 2 and less than or equal to N) output circuit, which is oneof the second through N^(th) output circuits, comprises: a K^(th)rectifier to generate a K^(th) output voltage by rectifying the voltagetransferred from the transformer; and a K^(th) switch to linearly switchan output voltage of the K^(th) rectifier according to a linear controlsignal of a K^(th) output voltage controller, which is one of the secondthrough N^(th) output voltage controllers.
 17. A multi-voltage powersupply including a transformer, a first output circuit to generate afirst output voltage using a voltage transferred to a secondary windingof the transformer, and a first output voltage controller to control avoltage supplied to a primary winding of the transformer according tothe first output voltage, the multi-voltage power supply comprising:second through N^(th) output circuits to generate second through N^(th)output voltages, respectively, using the voltage transferred to thesecondary winding of the transformer; and second through N^(th) outputvoltage controllers to control outputting the second through N^(th)output voltages, respectively, according to a switching operation byfeeding back the second through N^(th) output voltages, wherein a K^(th)(K is a positive integer greater than or equal to 2 and less than orequal to N) output circuit, which is one of the second through N^(th)output circuits, comprises: a K^(th) rectifier to generate a K^(th)output voltage by rectifying the voltage transferred from thetransformer; and a K^(th) switch to linearly switch an output voltage ofthe K^(th) rectifier according to a linear control signal of a K^(th)output voltage controller, which is one of the second through N^(th)output voltage controllers.
 18. The multi-voltage power supply of claim17, wherein the K^(th) rectifier comprises a^(th) diode and a K^(th)capacitor, which are connected in series, and together are connected inparallel to the secondary winding of the transformer, and a K^(th)output terminal is formed at both ends of the K^(th) capacitor to outputthe K^(th) output voltage.
 19. The multi-voltage power supply of claim17, wherein the K^(th) rectifier is either a half-wave rectificationcircuit or a full-wave rectification circuit.
 20. The multi-voltagepower supply of claim 18, wherein the K^(th) switch comprises a metaloxide semiconductor field effect transistor (MOSFET), a gate of which isconnected to an output terminal of the K^(th) output voltage controllerand the other terminals of which are connected between the K^(th) diodeand the K^(th) capacitor.
 21. The multi-voltage power supply of claim18, wherein the K^(th) switch comprises a bipolar junction transistor(BJT).
 22. The multi-voltage power supply of claim 17, wherein theK^(th) (K is a positive integer greater than or equal to 2 and less thanor equal to N) output voltage controller, which is one of the secondthrough N^(th) output voltage controllers, comprises: a K^(th) outputvoltage detector to detect a K^(th) output voltage; a K^(th) errordetector to compare the K^(th) output voltage detected by the^(th)output voltage detector to a predetermined reference voltage and outputan error value according to the comparison result; a K^(th) frequencysynchronization unit to synchronize a ramp signal provided from theoutside with a switching frequency of the primary winding of thetransformer; and a K^(th) pulse width modulator (PWM) to compare thesignal output from the K^(th) error detector to the synchronized rampsignal output from the^(th) frequency synchronization unit and output aK^(th) switching control signal to control a switching operation of theK^(th) switch.
 23. The multi-voltage power supply of claim 22, whereinthe^(th) output voltage detector is a voltage divider circuit.
 24. Themulti-voltage power supply of claim 22, wherein the reference voltage isgenerated by a resistor and a zener diode, which are connected between apredetermined voltage source and ground.
 25. The multi-voltage powersupply of claim 22, wherein the K^(th) output voltage controller furthercomprises: a K^(th) compensation circuit to provide a compensationcircuit using negative feedback, the K^(th) compensation circuit beingconnected in parallel to an output terminal of the K^(th) error detectorand an input terminal of the K^(th) error detector to which the K^(th)output voltage is applied and comprising: a resistor and a capacitor,which are connected in series.
 26. The multi-voltage power supply ofclaim 17, wherein a primary circuit of the transformer comprises acurrent source type switching circuit, which comprises a first switchperforming a switching operation using a first control signal input fromthe first output voltage controller.
 27. The multi-voltage power supplyof claim 26, wherein the current source type switching circuit isconfigured as one of a flyback type, an active clamp flyback type, ahalf-bridge flyback type, and a series resonance type.
 28. Themulti-voltage power supply of claim 26, wherein the current source typeswitching circuit further comprises: a snubber circuit to prevent aleakage inductance of the transformer.
 29. The multi-voltage powersupply of claim 17, wherein the first output circuit comprises arectifier to rectify the voltage transferred from the transformer. 30.The multi-voltage power supply of claim 29, wherein the rectifier iseither a half-wave rectification circuit or a full-wave rectificationcircuit.
 31. An image forming device comprising a multi-voltage powersupply including a transformer, a first output circuit to generate afirst output voltage using a voltage transferred to a secondary windingof the transformer, and a first output voltage controller to control avoltage supplied to a primary winding of the transformer according tothe first output voltage, the multi-voltage power supply comprising:second through N^(th) output circuits to generate second through N^(th)output voltages, respectively, using the voltage transferred to thesecondary winding of the transformer; and second through N^(th) outputvoltage controllers to control outputting the second through N^(th)output voltages, respectively, according to a switching operation byfeeding back the second through N^(th) output voltages, wherein a K^(th)(K is a positive integer greater than or equal to 2 and less than orequal to N) output circuit, which is one of the second through N^(th)output circuits, comprises: a K^(th) rectifier to generate a K^(th)output voltage by rectifying the voltage transferred from thetransformer; and a K^(th) switch to linearly switch an output voltage ofthe K^(th) rectifier according to a linear control signal of a K^(th)output voltage controller, which is one of the second through N^(th)output voltage controllers.
 32. A method of providing a multi-voltagepower supply using a transformer, the method comprising: generating afirst output voltage using a voltage transferred to a secondary windingof the transformer; controlling a voltage supplied to a primary windingof the transformer according to the first output voltage; generatingsecond through^(th) output voltages using the voltage transferred to thesecondary winding of the transformer; individually controlling tolinearly output the second through N^(th) output voltages byrespectively feeding back the second through N^(th) output voltages,generating a K^(th) output voltage by rectifying the voltage transferredfrom the transformer, where K is a positive integer greater than orequal to 2 and less than or equal to N; and linearly switching a K^(th)rectified output voltage according to a linear control signal of aK^(th) output voltage controller, which is one of a second throughN^(th) output voltage controllers.
 33. A method of providing amulti-voltage power supply using a transformer, the method comprising:generating a first output voltage using a voltage transferred to asecondary winding of the transformer; controlling a voltage supplied toa primary winding of the transformer according to the first outputvoltage; generating second through N^(th) output voltages using thevoltage transferred to the secondary winding of the transformer;individually controlling outputting the second through N^(th) outputvoltages according to a switching operation by respectively feeding backthe second through N^(th) output voltages, generating a K^(th) outputvoltage by rectifying the voltage transferred from the transformer,where K is a positive integer greater than or equal to 2 and less thanor equal to N; and linearly switching a K^(th) rectified output voltageaccording to a linear control signal of a K^(th) output voltagecontroller, which is one of a second through N^(th) output voltagecontrollers.
 34. A multi-voltage power supply including a transformer, afirst output circuit to generate a first output voltage using a voltagetransferred to a secondary winding of the transformer, and a firstoutput voltage controller to control a voltage supplied to a primarywinding of the transformer according to the first output voltage, themulti-voltage power supply comprising: a plurality of output circuitslocated on a side of the secondary winding of the transformer; aplurality of controllers to independently control a linear outputvoltage of each of the output circuits, by feeding back the outputvoltages, a plurality of rectifiers to independently generate outputvoltages by rectifying the voltage transferred from the transformer; anda plurality of switches to independently linearly switch output voltagesof the plurality of rectifiers according to linear control signals of aplurality of output voltage controllers.
 35. A multi-voltage powersupply including a transformer, a first output circuit to generate afirst output voltage using a voltage transferred to a secondary windingof the transformer, and a first output voltage controller to control avoltage supplied to a primary winding of the transformer according tothe first output voltage, the multi-voltage power supply comprising: aplurality of output circuits located on a side of the secondary windingof the transformer; a plurality of controllers to independently controlan output voltage of each of the output circuits, according to aswitching operation by feeding back the output voltages, a plurality ofrectifiers to independently generate output voltages by rectifying thevoltage transferred from the transformer; and a plurality of switches toindependently linearly switch output voltages of the plurality ofrectifiers according to linear control signals of a plurality of outputvoltage controllers.